Method and apparatus for transporting liquefied natural gas

ABSTRACT

Liquefied natural gas is transported by subcooling the liquefied natural gas below a temperature at which it has a vapor pressure equal to atmospheric pressure, loading the subcooled liquefied natural gas into an insulated vacuum vessel in a transporting means, transporting the subcooled liquefied natural gas in said insulated vacuum vessel to a destination, without refrigerating the liquefied gas, during a time period such that the liquefied natural gas arrives at the destination at a temperature no warmer than -260*F. and, unloading the liquefied natural gas at the destination. The liquefied natural gas while subcooled is unloaded and stored at about atmospheric pressure in an insulated tank without added refrigeration.

United States Patent 1191 .Reiche METHOD AND APPARATUS FOR TRANSPORTING LIQUEFIED NATURAL GAS [75] Inventor: Robert Fredrick Reiche, Wheaton,

[21] Appl. No.: 272,127

52 us. (:1. 62/55, 62/100 [51] Int. Cl. Fl7c 7/02 [58] Field of Search 62/55, 100, 268

[56] References Cited UNITED STATES PATENTS 2,975,604 3/1961 McMahon 62/55 x 3,159,004 12/1964 Keith l 62/55 x 3/1961 Morrison 62 55 x Jan. 8, 1974 I Primary ExaminerMey er Perlin Assistant Examiner-Ronald C. Capossela Ave /Eye Q rEmLMQKQQlLSh P & K1959 5 7 ABSTRACT Liquefied natural gas is transported by subcooling the liquefied natural gas below a temperature at which it has a vapor pressure equal to atmospheric pressure, loading the subcooled liquefied natural gas into an insulated vacuum vessel in a transporting means, transporting the subcooled liquefied natural gas in said insulated vacuum vessel to a destination, without refrigerating the liquefied gas, during a time period such that the liquefied natural gas arrives at the destination at a temperature no warmer than -26()F, and, unloading the liquefied natural gas at the destination. The liquefied natural gas while subcooled is unloaded and stored at about atmospheric pressure in an insulated tank without added refrigeration.

6 Claims, 2 Drawing Figures METHOD AND-APPARATUS FOR- TRANSPORTING .LlQUEFIED NATURAL GAS nient distribution point where it can be stored and later vaporized for use when needed.

Liquefied natural gas as presently transported is at a temperature of 260F. or warmer and a pressure equal to atmospheric pressure or higher. Even though the liquefied natural gas is transported in insulated tanks or vessels, the normal heat leak causes substantial quantities of vapor to be released. The vapors must be vented to the atmosphere and be lost or be reliquefied by means of refrigeration apparatus accompanying the transportation means and the liquid returned to the vessel or tank. Venting the vapors to the atmosphere is dangerous and constitutes an undesirable economic loss. Equiping the transportation means with refrigeration apparatus is expensive and, in the case of a breakdown, wouldnecessitate venting the vapor to the atmosphere. There is accordingly a need for alternative methods and apparatus useful therein for transporting liquefied natural gas.

According to the present invention there is provided a method or process of transporting liquefied natural gas comprising subcooling liquefied natural gas below a temperature at which it has a vapor pressure equal to atmospheric pressure, loading the subcooled liquefied natural gas into an insulated transportable vacuum vessel in a transporting means, transporting the subcooled liquefied natural gas in said insulated transportable vacuum vessel to a destination, without refrigerating the liquefied gas, during a time period such that the liquefiednatural gas arrives at the destination at a temperature no warmer than -260F., and a pressure no greater than atmospheric pressure and desirably at a pressure lower than atmospheric pressure so that no venting of vapor occurs. It is also desirable that the product arrive at the destination still subcooled so that unloading can be effected without refrigeration, and the product stored at about atmospheric pressure in an insulated tank. I

The liquefied natural gas can be subcooled a substantial time before his loaded into the vacuumvessel for transportation, or it can be subcooled just prior tosuch loading. It is advisable however to subcool at least part of the liquefied natural gasand store it in a vacuum storage vessel so that it is immediately available when needed forloading intoa transportation means such as aship, barge, truck or railroad car. Of course, the vacuum storage vessel must be strongenough to withstand the pressure differential between atmospheric pressure and the internal lower vapor pressure for storage of the subcooled liquefied natural gas until loaded for transportation.

' Prior to loading in the transportation means, the liquefied natural gas is advisably subcooled to a temperature such that it has a vapor pressure no greater than 10 psia which accordingly requires that the temperature of the liquefied, natural gas be.-270F. or colder. The extent of subcooling of the liquefied natural gas should however be coordinated-with the calculated heat leak during transportation, the vacuum to which the transportable vacuum vessel can be subjected, and the length of the journey or trip, so that theliquefied natural gas will arrive at the destination without vapor loss and a vapor pressureless than atmospheric pressure. Furthermore, it is advisable upon arrival at the destination that the liquefied natural gas be at a subcooled temperature adequate to provide enough refrigeration to compensate for heat leak during unloading so that it can be unloaded and stored, without added or supplemental refrigeration, at 260F. or colderand a pressure of 15 psia or less.

For a trip or voyage of about 2 weeks it is generally unnecessary to subcool the liquefied natural gas below 270F. unless it is desirable to have additional refrigeration available at the distination. For longer trips, or where there is high heat leak, the subcooled liquefied natural gas can be subcooled to 280F. or even to a lower temperature which gives a slush mixture of liquefied and frozen natural gas, such as at about -298F.

When loading the transportable insulated vacuum 'vessel, a single stream of subcooled liquefied natural gas can be fed thereto at a suitable temperature or alternatively two streams, one a subcooled stream and the other a stream at 26( )F. or warmer, can be combined and fed as a single subcooled stream to the transportable vacuum vessel. j

t The transportable insulated vacuum vessel in the transportation means must be constructed strong enough to safely withstand the pressure differential between the external atmospheric pressure and the significantly lower internal vapor pressure produced therein by the subcooled liquefied natural gas. The vessel is accordingly advisably custom made to handle the product under the conditions of temperature and pressure involved. If only moderate subcooling is used the vessel need not be as strong as one intended to withstand an internal pressure as low as about 1.5 psia as would be involved when a 40 percent slush of liquefied and fro- -zen natural gas at -298F. is transported in a vacuum vessel.

By subcooling the transported product prior to the trip, vapor loss is eliminated during the trip without the use of a refrigeration plant or other vapor recovery means provided heat leak does not raise the temperature of the liquefied natural gas above 260F. prior to arrival at the destination. By providing supplemental subcooling beyond that needed for the trip, upon ar-.

rival at the destination the product can be unloaded without vapor loss since the heat leak can be overcome by the subcooled temperature of the product being unloaded. Generally if the product arrives at the destination at a pressure less than 13 psia it will possess adequate subcooling for unloading without supplemental refrigeration.

Depending on the temperature of the product upon arrival at the destination, it can be stored in a vacuum vessel at a vapor pressure below atmospheric pressure, or in a tank designed to store the product at 260F. and at atmospheric pressure. However, it is advantageous to store the product at atmospheric pressure because a large storage tank can be built to store the product at such pressure for less cost than a large vacuum vessel.

In addition to permitting transportation of the product without vapor formation, subcooling of the product permits a greater load to be carried than in the case where the product is carried at a pressure higher than atmospheric pressure.

Although natural gas is referred to herein it should be understood that this term is intended to include methane and other gases which are substantially methane.

The invention will be described further in conjunction with the attached drawings in which:

FIG. 1 illustrates the loading of a ship with subcooled liquefied natural gas; and

FIG. 2 illustrates the transportation and unloading of subcooled liquefied natural gas from a ship.

So far as is practical, the same numbers will be used to identify the same or identical parts or elements in the drawings.

With reference to FIG. 1, insulated spherical vacuum vessel has an outer metal shell 11 and an inner metal shell 12 with insulation 13 between the shells. Legs 14 support vessel 10. Conduit 15, valve 16 and conduit 17 communicate with the interior of tank 10 for feeding subcooled liquefied natural gas thereto. Tank 10 is positioned on shore. Conduit 18, valve 19 and conduit 20 also communicate with the interior of tank 10 and are used to withdraw subcooled liquefied natural gas from the tank. Conduit 21 communicates with the vapor space in tank 10 and also with conduit 23 through control valve 22 for permitting vapor to flow in and out during loading and unloading of the tank. Vessel 10, while shown as spherical, can be cylindrical or some other suitable shape.

Ship 30 is equipped with a pair of spherical vacuum vessels 31, each mounted on a support 35. Each vessel 31 has an outer metal shell 32, an inner metal shell 33 and insulation 34 between the shells. Conduit 29 communicates with the bottom interior ofvessel 31 and conduit 27 through control .valve 28. It should be understood that vessels' 31 need not be spherical but can be cylindrical or some other suitable shape.

Liquefied natural gas from storage vessel 10 is loaded into vessels 31 in ship 30 by joining one end of conduit 25 to conduit 20 by means of coupling 24, and by joining the other end of conduit 25 to conduit 27 by coupling 26. After vessels 31 have been filled with subcooled liquefied natural gas valves 19 and 28 are closed.

Although ship 30 is shown equipped with a pair of insulated spherical vacuum vessels 31 for transporting subcooled liquefied natural gas it can, of course, be equipped with a single vessel or more than two vessels if desired.

After completing its voyage and upon arrival at its destination, the subcooled liquefied natural gas is unloaded from each of vessels 31 in ship 30 and stored in cylindrical tank 50. Tank 50, while shown cylindrical, can be spherical or some other suitable shape. Tank 50 has an outer metal shell 51, an inner metal shell 52 and insulation 53 between the shells. Tank 50 is designed to store liquefiednatural gas at -259F. and 14.7 psia. Conduit communicates with the interior bottom space of tank 50 and with conduit 38 through control valve 39. Conduit 36 is coupled at one end to conduit 27 through coupling 26, and it is coupled at the other end to conduit 38 by coupling 37. By means of the described conduit system liquefied natural gas is unloaded from vessels 31 in ship 30 and fed to storage tank 50. During loading of tank 50 vapor can be removed therefrom' by conduits 57 and 59 through control valve 58. After the ship has been unloaded valve 39 is closed.

Liquefied natural gas is removed as desired from storage tank 50 by conduits 54 and 56 through control valve 55. Control valve 55 is normally closed when the tank is being filled although it can be open and product removed simultaneously with filling. When product is removed from tank 50 valve 58 is open to allow a suitable gas to enter to avoid formation of a vacuum in the tank.

The following examples are presented to further illustrate the invention.

EXAMPLE I A ship having a cylindrical tank about 23 feet in diameter and about feet in length covered with 30 inches of perlite insulation is loaded with 1,381,000 pounds of liquefied natural gas subcooled to -269F. The tank internal pressure is 8 psia.

After a voyage of 338 hours at an ambient temperature of 1 15F. the ship will arrive at its destination without any venting of vapor or pressure build up in the vessel. Upon arrival the product will be at -260F. and 14.7 psia. The product is then unloaded and stored at -260F. and 14.7 psia with venting of vapor formed by heat leak during unloading.

By subcooling the transported product 2.3 percent more product can be carried than would be the case if the product were unloaded at -260F. and 14.7 psia with pressure build up from 0 to 5.1 psig during the voyage.

EXAMPLE 2 The ship of Example 1 is loaded with 1,435,000 pounds of a 50 percent liquid and frozen natural gas slush at -298F. and 1.55 psia. After the same voyage the ship will arrive at the destination with the product at -298F. and 1.55 psia. However, 6.3% more product can be carried by subcooling the product than would be possible if the product were loaded at -260F. and 14.7 psia with pressure build up from 0 to 5.1 psig during the voyage.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

l. A method of transporting liquefied natural gas comprising:

loading liquefied natural gas, which has been subcooled below a temperature at which it has a vapor pressure equal to atmospheric pressure, into an insulated vessel in a transporting means,

the pressure of the subcooled liquefied gas in the vessel being not more than about 10 psia upon completion of loading therein,

transporting the subcooled liquefied natural gas in said insulated vessel to a destination, without refrigerating the liquefied gas under pressure, during a time period such that the liquefied natural gas arrives at the destination at a temperature no warmer than 260F. and,

unloading the liquefied natural gas at the destination.

2. A method according to claim 1 in which the liquefied natural gas arrives subcooled at the destination, and the liquefied natural gas is unloaded and stored at about atmospheric pressure in an insulated tank without added refrigeration.

3. A method according to claim 1 in which the liquefied natural gas is subcooled to at least 270F. before being loaded into the insulated vessel.

4. A method according to claim 1 in which the liquefied natural gas is subcooled to a temperature at which a substantial part of the natural gas is solid.

5. A method according to claim 4 in which the liquefied natural gas is at a pressure less than 13 psia upon arrival at the destination.

6. A method of transporting liquefied natural gas comprising: 7

loading liquefied natural gas, which has been subcooled below a temperature at which it has a vapor pressure equal to atmospheric pressure, into an insulated storage vessel for storage at a pressure below atmospheric pressure,

. the pressure of the subcooled liquefied gas in the about atmospheric pressure in an-insulated tank. 

1. A method of transporting liquefied natural gas comprising: loading liquefied natural gas, which has been subcooled below a temperature at which it has a vapor pressure equal to atmospheric pressure, into an insulated vessel in a transporting means, the pressure of the subcooled liquefied gas in the vessel being not more than about 10 psia upon completion of loading therein, transporting the subcooled liquefied natural gas in said insulated vessel to a destination, without refrigerating the liquefied gas under pressure, during a time period such that the liquefied natural gas arrives at the destination at a temperature no warmer than -260*F. and, unloading the liquefied natural gas at the destination.
 2. A method according to claim 1 in which the liquefied natural gas arrives subcooled at the destination, and the liquefied natural gas is unloaded and stored at about atmospheric pressure in an insulated tank without added refrigeration.
 3. A method according to claim 1 in which the liquefied natural gas is subcooled to at least -270*F. before being loaded into the insulated vessel.
 4. A method according to claim 1 in which the liquefied natural gas is subcooled to a temperature at which a substantial part of the natural gas is solid.
 5. A method according to claim 4 in which the liquefied natural gas is at a pressure less than 13 psia upon arrival at the destination.
 6. A method of transporting liquefied natural gas comprising: loading liquefied natural gas, which has been subcooled below a temperature at which it has a vapor pressure equal to atmospheric pressure, into an insulated storage vessel for storage at a pressure below atmospheric pressure, the pressure of the subcooled liquefied gas in the storagE vessel being not more than about 10 psia upon loading therein, withdrawing subcooled liquefied natural gas from the storage vessel and loading it into an insulated transportable vessel in a transportation means, transporting the subcooled liquefied natural gas under vacuum in said insulated transportable vessel to a destination, without refrigerating the liquefied gas, during a time period such that the liquefied natural gas arrives at the destination at a temperature no warmer than -260*F., and unloading the liquefied natural gas at the destination, without refrigeration, and storing the product at about atmospheric pressure in an insulated tank. 